1. Field of the Invention
The present invention relates to a control device for a series-type hybrid automobile having a generator driven by an internal combustion engine and a battery as on-vehicle power sources which drive the power sources to run the automobile in accordance with an operational state of an accelerator pedal.
2. Description of Related Art
Electric vehicles have been developed as an alternative to automobiles using internal combustion engines which emit harmful exhaust gas. However, in the electric vehicle the energy storage capacity of a battery is small and a runnable distance during one charge cycle thereof is short. Accordingly, there has been a desire for a further increase in the running distance. A series-type hybrid automobile in which the electric automobile is further provided with a generator as an on-vehicle power source and an internal combustion engine for driving the generator has been disclosed as a substitute for the electric vehicle in Japanese Unexamined Patent Publication No. 62-64201.
However, although exhaust gas emissions are reduced in the series-type hybrid automobile in comparison with an automobile having only an internal combustion engine, it is necessary to mount both a battery and an internal combustion engine in the engine compartment. Therefore, it is necessary to mount a battery that is smaller than the one used in an electric automobile. Further, it is necessary to set a charged state of the battery at a sufficiently high level to provide a capacity large enough to sufficiently drive a motor for running the automobile during acceleration and on an uphill road.
As a result, when regenerative braking of the motor for running the automobile is performed where the automobile runs on a long downhill slope, the charging of the battery by current generated by the regenerative braking is promoted by which the battery easily reaches a saturated state of charging. Accordingly, even if the regenerative operation of the motor is performed after the battery has reached the saturated state of charging, the battery cannot be charged, a current level thereof is reduced and a braking force of the motor is lowered whereby a sufficient braking required for a vehicle cannot be provided.
As disclosed in Japanese Unexamined Patent Publication No. Sho. 62-64201, a resistor may be provided and current regenerated by the motor for running may be dissipated by the resistor. However, it is impossible for an engine compartment of limited size to provide insulation against high voltage applied to the resistor and at the same time provide a space large enough to radiate heat from the resistor.
Further, according to Japanese Unexamined Patent Publication No. Hei. 4-322105, when the capacity of a battery is large in regenerative braking of a motor for running, the braking force of the motor is provided to brake an internal combustion engine by making a regenerative current flow in a generator by using an inverter. However, it is necessary to provide a motor inverter for driving a motor, a generator inverter for driving a generator and a power source capacitor having large weight and large configuration to stabilize the operation of the respective inverters which increases the size and complexity of the control circuit.